*1921: George Polya. An indefinite linear random walk (unit steps forward/backwards by the results of a coin toss) or planar random walk (unit steps forward/backward/left/right by the results of tetrahedral die), will return to the origin with probability 1, more than once

*A 3D random walk, a return to the origin – even once – is not guaranteed, even if it goes on indefinitely. (In mathematical terms: the probability is less than 1).